Airborne Auxiliary Power Unit, abbreviated as APU, is a small turbine engine mounted on the tail of an aircraft. Its main function is to supply power and gas sources, with a few APUs capable of providing additive thrust to the aircraft. Specifically, before taking off from the ground, an aircraft may do not need to rely on ground power and gas source vehicles to start the aircraft as its main engine may be started via power supply from the APU. While on the ground, the APU also supplies power and compressed air to ensure lighting and air-conditioning in the cabin and cockpit. During take-off of an aircraft, the APU can serve as a backup power source. After the aircraft is landed, lighting and air-conditioning of the aircraft are still powered by the APU. The functions of APU determine that its stability directly affects flight cost and quality of service of the aircraft.
APU fuel assembly is an important component of APU. Once the fuel assembly fails, it will directly cause the APU unable to start, and thus cause grounding of the aircraft. Currently, there is not any effective way to maintain the APU fuel assembly except for breakdown maintenance, which inevitably causes aircraft delay and increases of maintenance costs.